1. Field of the Invention
The present invention relates to data transmission apparatus, data reception apparatus and medium used in transmission or reception of, for example, video data or audio data.
2. Description of the Related Art
Hitherto, as the digital interface for transferring digital video data or audio data, the IEEE 13 94 has been known.
This IEEE1394 is being developed as the interface for multimedia, and is the interface capable of transferring data requesting real-time handling such as video data and audio data within a specific delay time. In this interface, the data is transferred in the unit of packet.
In the IEEE1394, as the identification information for specifying the devices such as terminal and server, there is a concept known as node ID. In this node ID, any value from 0 to 62 can be used, and therefore up to 63 devices can be connected on one bus. In each bus, a bus ID can be added, so that up to 1023 buses can be connected.
The IEEE1394 supports two modes of transfer, that is, isochronous transfer used in transfer of data of which real time must be guaranteed such as video and audio data, and asynchronous transfer used in transfer of data of which guarantee of delay time of transfer is not required. In the isochronous transfer, when the packet is transmitted onto the transmission medium (bus), the channel number is added to the packet for distinguishing the packet from the others, and the transmission and reception of the packet are controlled on the basis of this channel number.
On the other hand, in the IEEE1394, all devices connected to the bus have a virtual 48-bit address space 901. In asynchronous transfer, this address space 901 is mutually read out, and written in, so that data transfer is realized. In part of this address space 901, a register used for the purpose of controlling the operation of each device is contained. The operating state of the device connected to the bus can be checked by reading out the control register of other device, and the device can be controlled by writing in a value in this control register as required.
So far, by using the IEEE1394, it has been attempted to develop the transport stream of MPEG2 (moving picture experts group), and the method of transfer of data of the DV which is the digital VCR(VTR) for household use. In this method, the isochronous transfer is employed in the transfer of video data and audio data.
Besides, for the purpose of controlling transmission and reception of video and audio data, a control register placed in the address space 901 in each device is used. This control register is called the PCR (plug control register). The data transmission apparatus such as server has oPCR 902 as register for output control, and the data reception apparatus such as terminal has iPCR as register for input control. FIG. 12 is a conceptual diagram showing any address space 901 possessed by the data transmission apparatus. In the IEEE1394, in the address space 901 of each device, the beginning address of the oPCR is fixed as FFFFF0000904h. The content of the oPCR 902 is shown in FIG. 13. Channel number 903 shown in FIG. 13 is a concept on transmission medium used in data transmission and reception.
The device for controlling transmission and reception of video and audio data can check the state of transmission or reception by reading out this PCR. It is also possible to instruct to start transmission or reception or to stop by writing into the PCR. When one device transmits or receives plural pieces of video data or audio data simultaneously, plural PCRs may be provided.
FIGS. 14(a) to 14(c) show formats of packets used in transfer of data of MPEG or DV by using the IEEE1394. FIG. 14(a) is a diagram showing the format of packet used in transfer of data.
As shown in the diagram, the packet header 904 in this packet includes the channel 905 of isochronous transfer and the information showing the size of packet (shown as data length 906 in FIG. 14(b)) as shown in FIG. 14(b). The other CIP header 907, as shown in FIG. 14(c), is used for the purpose of compensating for the information lacking in the packet header such as type of data. In the portion consecutive to this CIP header 907, the video data or audio data is contained and transferred.
As shown in FIG. 14(c), the format of the transmitted data, that is, the processing method is indicated by FMT 908 of the CIP header 907. That is, from the content of the FMT 908, the MPEG or DV can be identified. The node ID of the transmitting device is indicated by SID 909.
When the device receiving this data checks or controls the state of the transmitting device, first, the node ID of the transmitting device is identified by the SID 909, and the oPCR of the transmitting device is read out. Herein, if the transmitting device has plural oPCRs, by searching the oPCR which is transmitting the channel number being received, the corresponding oPCR can be determined. As a result, by reading out the content of the identified oPCR, the state of transmission is known, or the transmission can be stopped or other control is possible.
The data reception apparatus receiving such video data transmitted in the packet format reads the content of the FMT 908, and distinguishes the processing method of the received data, that is, whether the coding method is MEPG or DV. Then, for example, when the data coding method is judged to be MPEG, the data reception apparatus executes a series of processing such as decoding of the received data, by using the processing method corresponding to MPEG prepared in the memory. Or, using the exclusive processing circuit for MPEG, a series of processing such as decoding is conducted.
In such conventional constitution, however, in order to cope with any processing method (for example, coding method) used in the data transmission apparatus, the processing methods (for example, decoding method) corresponding to all processing methods must be prepared at the data reception apparatus side. It is not a particular problem as far as the variety of processing methods at the data transmission apparatus is small, but as the number of types of processing method at the data transmission apparatus side increases, the number of processing methods to be prepared at the data reception apparatus side increases, and a huge memory capacity is required.
Incidentally, if the video data is processed at the data transmission apparatus side by a completely new processing method not prepared at the data reception apparatus side, the data reception apparatus side, if receiving such video data, cannot process appropriately. Accordingly, in order to always cope with the data processed by new method, the prepared processing methods must be updated and increased frequently at the data reception apparatus side. That is, the scope of capability of processing the received data at the data reception apparatus was limited by the types of the processing methods prepared in the data reception apparatus.